Coated lens exhibiting substantially balanced reflectance

ABSTRACT

A coated optical lens includes a lens element and a coating on the surface of the lens element. The coating exhibits a substantially balanced reflectance from the center to a radius proximate the edge of the lens element. The term “substantially balanced reflectance” means that where the thickness of the coating varies across the surface of the lens, the lightness, hue and chroma of the reflectance vary in a balanced manner such that variations in visual appearance are either imperceptible or generally acceptable to an observer. For example, variations in chromatic attributes, such as hue, from the center to the edge of the lens may be balanced by a reduction in lightness from the center to the edge. Preferably, the lens element includes a surface of high curvature upon which the balanced reflectance coating is deposited.

The present invention relates to optical articles bearing a coatingwhich displays superior uniformity of reflection.

The optical articles according to the present invention are preferablyemployed in the preparation of articles such as optical lenses,including spectacle lenses, including sunglass lenses, visors, shields,glass sheets, protective screens, and the like.

Anti-reflection coatings are commonly deposited on ophthalmic andsunglass lenses in order to minimise spurious reflections, which bothdetract from the wearer's vision and are also cosmetically unpleasing.These coatings commonly consist of multilayer, dielectric films ofthicknesses chosen so that interference effects cause destructivecancellation of reflections over most of the visible spectrum.

A coating that is not anti-reflective and that changes the reflectanceof the lens can be described as a “mirror” coating. Such mirror coatingsare often used in the manufacture of sunglass lenses, to producefashionable lens colours.

When mirror and anti-reflection coatings are deposited on curvedsubstrates (such as ophthalmic lenses), regardless of the depositionmethod used (e.g. evaporative, sputtered, etc.) geometrical factorsresult in the coating thickness being non-uniform and varyingsystematically over the surface of the lens. The coating thickness istypically greatest where the surface of the substrate is most normal tothe incident flux of particles, and thinner where the surface faces theflux at an angle. For ophthalmic lenses, which are normally mounted withtheir centres facing the particle source, this means a coating that isthickest in the centre and that becomes thinner towards the edge of thelens element. This effect becomes more pronounced as the lens becomesmore highly curved.

The coating thickness variations manifest themselves as visiblevariations in the reflectance from the coated lens. The colour(specified by “lightness”, “hue” and “chroma”) of the residualreflection changes from the centre to the edge of the lens, an effectreferred to as “colour rolloff.” For lenses of normal curvature, thecolour rolloff is barely noticeable and cosmetically, the lenses areconsidered to be acceptable. However, for very highly curved lenses, thecolour rolloff is particularly noticeable and is generally considered tobe unsatisfactory.

One method proposed in the prior art to reduce colour rolloff is tomount the substrate on a “planetary rotation” stage, which spins thelens about its own axis at the same time that it rotates about anothercentral axis. The result of the complex substrate motion in thedeposition chamber is that the flux of coating material is more evenlydistributed over the surface of the lens, resulting in a coating that ismore uniform over the substrate than would otherwise be the case.Planetary rotation is not the only option—any substrate motion at allwill tend to reduce coating thickness non-uniformities. Unfortunately,implementing such substrate movement in the deposition chamber necessaryinvolves mechanical complexity and a likely decrease in the total numberof substrates that can be coated simultaneously in the apparatus, whichis a severe disadvantage in a commercial production process.

It would accordingly be a significant advance in the art if ophthalmiclenses could be provided with a coating or coatings of generalapplicability which could reduce the phenomenon of “colour rolloff”, butwithout the need for “planetary rotation” apparatus.

Accordingly, it is an object of the present invention to overcome, or atleast alleviate, one or more of the difficulties or deficiencies relatedto the prior art.

Accordingly, in a first aspect of the present invention there isprovided a coated optical lens including

a lens element; and

a coating on a surface of the lens element exhibiting a substantiallybalanced reflectance from the centre to a radius proximate the edge ofthe lens element.

The lens element may preferably include a surface of high curvature,upon which the balanced reflectance coating is deposited. By the term“surface of high curvature”, we mean a surface having a base curveapproximately 6 Dioptres (D) or greater, preferably 6 D to 20 D, morepreferably approximately 8 D to 16 D.

The lens element may be either optically clear or tinted (lightabsorbing), such as a sunglass lens, ophthalmic lens element, visor orthe like.

By the term “ophthalmic lens element”, as used herein, we mean all formsof individual refractive optical bodies employed in the ophthalmic arts,including, but not limited to, lenses, lens wafers and semi-finishedlens blanks requiring further finishing to a particular patient'sprescription.

The visual appearance of the coated optical lens in reflected light-canbe quantified by measuring its reflectance spectrum in aspectrophotometer. It is well known that the reflectance of thin filmcoatings tends to vary with the angle of the incident light. When wespeak of the reflectance from the lens we imply the reflectance of lightincident at angles of 0 to approximately 30 degrees to the normal to thesurface of the lens, as would typically be the case for the reflectedlight seen by an observer standing directly in front of a person wearingthe coated lenses as spectacles. This spectral information may bereduced to three colour coordinates—a “lightness” correspondingprimarily to the luminous intensity of the reflected light, and twochromatic attributes, “hue” and “chroma”, corresponding to the generalcolour (e.g. “red, “blue”, “green” etc.) and its vividness. (“TheMeasurement of Appearance”, 2^(nd) ed., R. S. Hunter and R. W. Harold,Wiley, New York, 1987).

By the term “substantially balanced reflectance” we mean that where thethickness of the coating varies across the surface of the lens, thelightness, hue and chroma of the reflectance vary in a balanced mannersuch that variations in visual appearance are either imperceptible orgenerally acceptable to an observer. For example, variations inchromatic attributes, such as hue, from the centre to the edge of thelens may be balanced by a reduction in lightness from the centre to theedge.

Perceived variations in appearance may be quantified by calculating “CMCcolour differences,” as developed by the Colour Measurement Committee ofthe Society of Dyers and Colourists. A CMC colour variation ofΔE_(CMC(2:1))=1 is the limit of acceptability for textiles. Applicantshave found that this is too stringent a tolerance for anti-reflection ormirror coated lenses in the ophthalmic industry. Variations betweenanti-reflection coated lenses of approximately 3 or less are acceptableand Applicants have observed that colour differences of up to 3-11 mayexist across a lens that has an acceptably uniform appearance.Variations of up to 20 may exist in lenses that are visibly non-uniformin colour, yet that are still acceptable in appearance.

The normal incidence reflectance spectrum of a highly curved (16dioptre) lens coated with a typical commercial anti-reflection coatingis shown in FIG. 1.

The reflectance of light of essentially normal incidence measured at thecentre of the tens element is low in the visible spectrum (roughly380-780 nm), but is significantly greater for longer wavelengths. Towardthe edge of the lens element (e.g. at a radius of 20 mm from thecentre), the total coating thickness may be reduced to 80% of thethickness at the centre of the lens. This is due to the curvature of thelens and the geometry of the deposition system as described above. Asshown in the figure, the spectrum shifts to the left relative to thespectrum from the centre of the lens. This is a well-known phenomenon tothose familiar with the art and theory of thin films. As a consequence,the higher reflectance “red tail” seen in FIG. 1 moves further into theregion of spectral sensitivity of the human eye and causes theappearance of the lens to redden toward the edges. The CMC colourdifference (for CIE illuminant C) between the centre of the lens and atthe radius of 20 mm is ΔE_(CMC(2:1))=27. The lens displays substantialcolour roll-off, changing from faint green in the centre to brightred/orange at the edges and is unacceptable.

In contrast, the balanced reflectance coating according to the presentinvention has a substantially more uniform appearance from the centre tothe edge of the lens element (see FIG. 2 below).

FIG. 2 compares the reflectance spectra at the centre and at a radialdistance of 20 mm from the centre on a 16 dioptre lens now coated withthe roll-off-resistant coating. In contrast to the previous standardanti-reflection coating, this coating (at the centre of the lens)exhibits substantially lower photopic reflectance at longer wavelengths.Indeed, it is anti-reflective beyond 880 nm. When the coating thicknessreduces away from the centre of the lens and the reflectance spectrumshifts to the left, relatively little intensity is introduced in the redregion of the spectrum. The CMC colour difference (for CIE illuminant C)between the centre of the lens and at the radius of 20 mm isΔE_(CMC(2:1))=10. The lens displays relatively little colour roll-off.The lens changes from light blue in the centre to pale blue/purple atthe edges and is quite acceptable.

This may be achieved, inter alia, by providing a balanced reflectancecoating for a lens element which, in use, exhibits a substantiallyconstant low photopic reflectance in the red-to-infra-red wavelengthrange of approximately 620 to 880 nm proximate the centre of the lenselement.

Preferably, the photopic reflectance is less than approximately 3%. Thereflectance is preferably low where the eye is most sensitive, in theregion of approximately 550 nm.

The low reflectance in the near infra-red spectrum is clearly animportant characteristic of the balanced reflectance coating, but forcertain coloured coatings this alone may not ensure that it displaysacceptable colour roll-off e.g. on a highly curved lens. For example, ifthe coating displays a red colour in the centre of the lens, even if thereflectance in the near infra-red is low, the colour will roll throughyellow and green as the thickness rolls off from centre to edge of thelens. If a uniform hue is desired the roll-off will not be acceptable.If, however, a multicoloured lens, which is still functionallyanti-reflective as its hue changes is the desired result, then the lenswill exhibit acceptable colour roll-off, because the colour roll-off isbalanced by luminous reflectance roll-off (as opposed to hue) which isacceptable.

The balanced reflectance coating is not restricted to functioning as ananti-reflection coating. The balance of reflectance coating mayalternatively or in addition function as a light absorbing, or tintcoating, in which case it may also have an asymmetric reflectance, suchthat from the wearer's side of the lens element the coating isanti-reflective. The balanced reflectance coating may also function as areflective or mirror coating.

The balanced reflectance coating may exhibit a substantially constantlow photopic reflectance in the wavelength range of approximately 620 to880 nm, the photopic reflectance preferably being less thanapproximately 1.5%.

The balanced reflectance coating may, for example, exhibit a reflectedcolour difference from the centre to a radius of approximately 20 mm onthe lens surface of less than approximately 11 CMC colour differenceunits.

Alternatively, the coating may exhibit a reflected colour difference(ΔE) from the centre to a radius of approximately 20 mm on the lenssurface of greater than approximately 11 CMC colour difference units,the colour difference being balanced by a complementary reduction inluminous intensity.

More preferably the coating exhibits a reflected colour difference (ΔE)of from approximately 11 to 20 CMC colour difference units.

In this embodiment the coating is preferably a multicoloured,anti-reflective coating.

In accordance with the present invention, one or both surfaces of anoptical lens element may be coated with the balanced reflectancecoating.

In a preferred aspect, the lens element may be of generally ovalineshape and is located on the surface of a sphere whose radius ofcurvature corresponds to 11 D or above, a toroid where the horizontalradius of curvature corresponds to 11 D or above, or a surface where theradius of curvature changes across at least one section of the lensaperture.

The lens element may be of the type described in International PatentApplication PCT/AU98/00872 “Spectacle Frames” to Applicants, the entiredisclosure of which is incorporated herein by reference; or inAustralian Provisional Patent Application PP4748 “Optical Lens” toApplicants, the entire disclosure of which is incorporated herein byreference.

It will be appreciated that while the balanced reflectance coating canbe beneficially applied to a highly curved lens, its use is notrestricted to such an application. For instance, the balancedreflectance coating can be applied in a situation where the depositionprocess is imperfectly controlled. In such a case, variations in coatingthickness caused by the deposition process (rather than the highcurvature of the lenses being coated) are less visible, by virtue of theoptical properties of the balanced reflectance coating.

Where the lens element is an ophthalmic lens element, the ophthalmiclenses may be formed from a variety of different lens materials, andparticularly from a number of different polymeric plastic resins. Acommon ophthalmic lens material is diethylene glycol bis(allylcarbonate) or CR39 (PPG Industries). Lens materials with higherrefractive indices are now growing in popularity. Other examples of lensmaterials that may be suitable for use with the invention include otheracrylics, other allylics, styrenics, polycarbonates, vinylics,polyesters and the like.

In a preferred aspect, the balanced reflectance coating may be amulti-layer coating. The balanced reflectance coating may include aplurality of layers, the thickness and/or number of which being selectedto reduce the phenomenon of “colour rolloff”. The balanced reflectancecoating may further provide an interference effect, e.g. ananti-reflective or mirror effect.

More preferably the balanced reflectance coating includes a plurality oflayers, wherein the thickness and/or number of the respective layers areselected to provide a substantially balanced reflectance in response tovisual effects generated by variations in thickness of the coating inuse, for example, as may occur when applied to a surface of a lens ofhigh curvature.

In this embodiment, the coating may include a plurality of layers ofdiffering refractive index wherein the thickness and/or number of therespective layers are selected to balance the variation of anycombination of reflectance lightness, hue and chroma.

More preferably, the balanced reflectance coating exhibits asubstantially constant low photopic reflectance in the red-to-infra-redwavelength range of approximately 620 to 880 nm, the photopicreflectance preferably being less than approximately 3%. The reflectanceis preferably low where the eye is most sensitive, in the region ofapproximately 550 nm, so that the coating has an anti-reflectivecharacter.

The number and/or thickness of the layers may be selected utilisingsuitable computer software, adapted to minimise the variation of anycombination of reflected lightness, hue or chroma accompanyingvariations in coating thickness.

In addition other desired coating properties may be provided at the sametime.

The layers of differing refractive index may be formed from any suitablematerial. The low and high refractive index layers may be formed of adielectric material. Preferably the dielectric layers may be formed frommetal oxides, fluorides or nitrides and diamond-like carbon. Preferablythe dielectric material is selected from one or more of Al₂O_(3,)BaTiO_(3,) Bi₂O_(3,) B₂O_(3,) CeO_(2,) Cr₂O_(3,) Ga₂O_(3,) GeO_(2,)Fe₂O_(3,) HfO_(2,) In₂O_(3,) Indium-tin oxide, La₂O_(3,) MgO, Nd₂O_(3,)Nb₂O_(5,) Pr₂O_(3,) Sb₂O_(3,) Sc₂O_(3,) SiO, SiO_(2,) SnO_(2,) Ta₂O_(5,)TiO, TiO_(2,) TiO_(3,) WO_(3,) Y₂O_(3,) Yb₂O_(3,) ZnO, ZrO_(2,) AlF_(3,)BaF_(2,) CaF_(2,) CdF_(2,) CeF_(3,) HfF_(4,) LaF_(3,) LiF, MgF_(2,) NaF,Na₃AlF_(5,) Na₅Al₃Fl_(14,) NdF_(3,) PbF_(2,) PrF_(3,) SrF_(2,) ThF_(4,)ZrF_(4,) Si₃N_(4,) AlN.

Optionally the dielectric materials may include standard dopants, forexample other materials or metal compounds. See for example U.S. Pat.No. 3,914,516 “Balzers”.

Alternatively, the layers of differing refractive index may be formedfrom layers of polymeric materials having varying refractive index. Suchpolymeric materials may be produced utilising plasma enhanced chemicalvapour deposition (PECVD) techniques. See for example European patent EP0916683 “Clariant International Ltd”.

A silica (SiO₂) or magnesium fluoride (MgF₂) material is preferred forthe lower index layers.

The higher refractive index layer may exhibit a refractive index ofapproximately 2.0 or greater. A titanium oxide (TiO₂) or combination oftitanium and praseodymium oxide (TiO₂+Pr₂O₃) is preferred for the higherindex layer(s). Such a combination may have a refractive index at 500 nmof approximately 2.15.

In a preferred form, the balanced reflectance coating may include atotal of 2 to 6 alternating layers of differing refractive index,preferably 4 to 6 alternating layers.

Alternatively, the balanced reflectance coating may be formed ofdielectric and metallic layers. Preferably the dielectric layers may beformed from metal oxides, fluorides or nitrides and diamond-like carbon.Preferably the dielectric material is selected from one or more ofAl₂O_(3,) BaTiO_(3,) Bi₂O_(3,) B₂O_(3,) CeO_(2,) Cr₂O_(3,) Ga₂O_(3,)GeO_(2,) Fe₂O_(3,) HfO_(2,) In₂O_(3,) Indium-tin oxide, La₂O_(3,) MgO,Nd₂O_(3,) Nb₂O_(5,) Pr₂O_(3,) Sb₂O_(3,) Sc₂O_(3,) SiO, SiO_(2,) SnO_(2,)Ta₂O_(5,) TiO, TiO_(2,) TiO_(3,) WO_(3,) Y₂O_(3,) Yb₂O_(3,) ZnO,ZrO_(2,) AlF_(3,) BaF_(2,) CaF_(2,) CdF_(2,) CeF_(3,) HfF_(4,) LaF_(3,)LiF, MgF_(2,) NaF, Na₃AlF_(6,) Na₅Al₃Fl_(14,) NdF_(3,) PbF_(2,) PrF_(3,)SrF_(2,) ThF_(4,) ZrF_(4,) Si₃N_(4,) AlN. Preferably the metallicmaterial is selected from the metals, metal oxides or nitrides of one ormore of Aluminium (Al), Chromium (Cr), Niobium (Nb), Nickel (Ni),Palladium (Pd), Tin (Sn), Tantalum (Ta), Titanium (Ti), Tungsten (W) orZirconium (Zr).

A silica (SiO₂) or magnesium fluoride (MgF₂) material is preferred forthe low index layers.

Chromium (Cr) or Niobium (Nb) is preferred for the metallic layers.

The optical lens according to the present invention may further includeone or more additional coatings. Accordingly in a further aspect of thepresent invention there is provided a multi-coated optical lensincluding

a lens element;

a coating on a surface of the lens element exhibiting a substantiallybalanced reflectance from the centre to a radius proximate the edge ofthe lens element; and

one or more secondary coatings which provide a desirable optical and/orchemical and/or mechanical property to the optical article.

Preferably, the lens element includes a surface of high curvature uponwhich the balanced reflectance coating is deposited.

More preferably, in use, the coating exhibits a reflected colourdifference from the centre to a radius of approximately 20 mm on thelens surface of less than approximately 11 CMC colour difference unitsor less.

Alternatively, the coating exhibits a reflected colour difference (ΔE)from the centre to a radius of approximately 20 mm on the lens surfaceof greater than approximately 11 CMC colour difference units, the colourdifference being balanced by a complementary reduction in luminousintensity

The secondary coating(s) may overlay or underlay the balancedreflectance coating or be applied to a second surface of the lenselement.

The secondary coating(s) may be of any suitable type. The secondarycoating(s) may be selected from one or more of an anti-reflective,abrasion resistant, impact-resistant or hydrophobic coating. Anabrasion-resistant coating is preferred. The combination of an abrasionresistant coating and an anti-reflective coating is particularlypreferred.

Applicants have further noted that, where the balanced reflectancecoating is applied to both surfaces of an ophthalmic lens element it ispossible to improve optical performance, including colour uniformity, onhighly curved substrates even further by balancing the colour variationsbetween the two surfaces. It may further be possible to reduce oreliminate other optical aberrations, such as “ghost images” which may begenerated by reflective coatings.

Accordingly, in a preferred aspect of the present invention, there isprovided a multicoated optical lens including

a lens element;

a first coating on the front surface of the lens element; and

a secondary coating on the back surface of the lens element; the firstand second coatings in combination exhibiting a substantially balancedreflectance from the centre to a radius proximate the edge of the lenselement.

The first coating on the front surface may be similar to the balancedreflectance coatings described above.

The secondary coating may function to reduce optical aberrations, suchas “ghost images”. The secondary coating exhibits a difference inlightness or hue relative to the first coating, for example a reductionin lightness.

Alternatively, the secondary coating may exhibit a reflectance peakwhich is spectrally displaced with respect to the reflectance peak ofthe first coating. The secondary coating consequently exhibits adifferent hue to the first coating.

In a further preferred aspect of the present invention, one or bothsurfaces of the optical article may be subjected to a surface treatmentto improve bondability and/or compatibility of the balanced reflectanceand/or secondary coating. The surface treatment may be selected from oneor more of the group consisting of plasma discharge, corona discharge,glow discharge, ionising radiation, UV radiation, flame treatment andlaser, preferably excimer laser treatment. A plasma discharge treatmentis preferred. The surface treatment, alternatively or in addition, mayinclude incorporating another bonding layer, for example a layerincluding a metal or metal compound selected from the group consistingof one or more of Chromium, Nickel, Tin, Palladium, Silicon, and/oroxides thereof.

The optical article may be a sunglass lens of the wrap-around or visortype, for example of the type described in International PatentApplication PCT/AU97/00188 “Improved Single Vision Lens” to Applicants,the entire disclosure of which is incorporated herein by reference.

In a further aspect of the present invention, there is provided a methodfor preparing a coated optical lens, which method includes

providing

a lens element,

a coating exhibiting a substantially balanced reflectance from the

centre to a radius proximate the edge of the lens element; and

depositing the coating on a surface of the lens element.

Preferably the lens element includes a surface of high curvature uponwhich the balanced reflectance coating is deposited. More preferably thebalanced reflectance coating is applied to both surfaces of the lenselement.

According to the present invention it has been found that, following themethod mentioned above, it is possible to achieve a relatively thin,balanced reflectance coating with consequent advantages in both opticaland mechanical properties.

Preferably the method further includes

providing

a lens element,

a high refractive index material, and

a low refractive index material;

depositing overlapping layers of high and low refractive index materialon a surface of the optical lens element, wherein the thickness and/ornumber of the respective layers are selected to balance the variation ofany combination of reflected lightness (luminous intensity), hue andchroma.

The balanced reflectance coating may further provide a desiredinterference effect, preferably an anti-reflective effect or mirroreffect.

In a preferred aspect the high and low refractive index materials,preferably TiO₂, Pr₂O₃/TiO₂ and SiO₂, are deposited as alternatinglayers.

Alternatively, the method may include

providing

a lens element;

a dielectric material selected from one or more of Al₂O_(3,) BaTiO_(3,)Bi₂O_(3,) B₂O_(3,) CeO_(2,) Cr₂O_(3,) Ga₂O_(3,) GeO_(2,) Fe₂O_(3,)HfO_(2,) In₂O_(3,) Indium-tin oxide, La₂O_(3,) MgO, Nd₂O_(3,) Nb₂O_(5,)Pr₂O_(3,) Sb₂O_(3,) Sc₂O_(3,) SiO, SiO_(2,) SnO_(2,) Ta₂O_(5,) TiO,TiO_(2,) TiO_(3,) WO_(3,) Y₂O_(3,) Yb₂O_(3,) ZnO, ZrO_(2,) AlF_(3,)BaF_(2,) CaF_(2,) CdF_(2,) CeF_(3,) HfF_(4,) LaF_(3,) LiF, MgF_(2,) NaF,Na₃AlF_(6,) Na₅Al₃Fl_(14,) NdF_(3,) PbF_(2,) PrF_(3,) SrF_(2,) ThF_(4,)ZrF_(4,) Si₃N_(4,) AlN, or diamond-like carbon; and

a metallic material selected from the metals, metal oxides or nitridesof one or more of Aluminium (Al), Chromium (Cr), Niobium (Nb), Nickel(Ni), Palladium (Pd), Tin (Sn), Tantalum (Ta), Titanium (Ti), Tungsten(W) or Zirconium (Zr)

depositing overlapping layers of dielectric and metallic material on asurface of the optical lens element, the number and/or thickness of therespective layers being selected to balance the variation of anycombination of reflected lightness, hue and chroma.

Preferably, the dielectric material is magnesium fluoride (MgF₂) orsilica (SiO₂); and the metallic material is Niobium (Nb) or Chromium(Cr).

The deposition step may be a vacuum deposition step. The deposition stepmay be conducted in a coating apparatus. A box coater or sputter coatermay be used.

The balanced reflectance coating may preferably be formed on thesurfaces of the substrate according to the process and the box coatersas described in the Italian Patent No. 1.244.374 the entire disclosureof which is incorporated herein by reference.

In accordance with said method, the various layers of the balancedreflectance coating may be deposited in subsequent steps utilising avacuum evaporation technique and exposing the growing layers to abombardment of a beam of ions of inert gas.

Moreover, in accordance with the preferred method, the deposition of thelayers may be achieved at a low temperature (generally below 80° C.),using an ion beam having a medium intensity (meaning the average numberof ions that reach the substrate) included between approximately 30 and100 μA/cm2 and the energy included between approximately 50 and 100 eV.

Further characteristics and advantages of the present invention will beapparent from the following description of drawings and examples ofembodiments of the present invention, given as indicative but notrestrictive.

In the figures:

FIG. 1 illustrates a measured reflectance spectrum (for light at normalincidence) of a lens coated on both sides with a known multilayer,anti-reflection coating.

FIG. 2 illustrates a measured reflectance spectrum (for light at normalincidence) of a lens coated on both sides with a multilayer,ant-reflection coating corresponding to the present invention.

FIG. 3 compares the typical reflectance spectra measured at the centreand at a radius of 20 mm on a 16 dioptre polycarbonate lens coated onboth sides with the balanced reflectance coating.

FIG. 4 illustrates the calculated reflectance spectrum for a CR39 lenscoated on both sides with the balanced reflectance coating, as well asthe reflectance spectrum when the coating thickness is reduced by 20%.

FIG. 5 illustrates the corresponding calculated reflectance spectra fortinted CR39 lenses coated on the front surface with the balancedreflectance coatings.

EXAMPLE 1

Standard Anti-reflection Coating

FIG. 1 illustrates a measured reflectance spectrum (for light at normalincidence) of a 16 dioptre polycarbonate lens coated on both sides withan abrasion-resistant coating and a typical commercial multilayer,anti-reflection coating.

The reflectance at the centre of the lens is low in the visible spectrum(roughly 380-780 nm), but is significantly greater for longerwavelengths. Toward the edge (at a radius of 20 mm), the total coatingthickness is reduced to 80% of the thickness at the centre of the lens.This is due to the curvature of the lens and the geometry of thedeposition system, a Satis 1200 evaporative box coater. As shown in thefigure, the spectrum shifts to the left relative to the spectrum fromthe centre of the lens. This is a well-known phenomenon to thosefamiliar with the art and theory of thin films. As a consequence, thehigher reflectance “red tail” seen in FIG. 1 moves further into theregion of spectral sensitivity of the human eye and causes theappearance of the lens to redden toward the edges. The CMC colourdifference (for CIE illuminant C) between the centre of the lens and atthe radius of 20 mm is ΔE_(CMC(2:1))=27. The lens displays substantialcolour roll-off, changing from faint green in the centre to brightred/orange at the edges and is unacceptable.

TABLE 1 Standard commercial anti-reflection coating Layer Thickness (nm)Polycarbonate substrate SiO2 173 Pr2O3/TiO2 (n(500 nm) = 2.05) 23.4 SiO218.7 Pr2O3/TiO2 (n(500 nm) = 2.05) 93.2 SiO2 82.6 Hydrophobic 10

EXAMPLE 2

Balanced Reflectance Anti-reflection Coating with Low Variation in Hue

Table 2 shows the optical design for an anti-reflection coating whosereflected colour, particularly its hue, is robust to colour roll-offwhen its thickness varies.

FIG. 2 compares the reflectance spectra measured at the centre and at aradius of 20 mm on a 16 dioptre CR39 lens coated on both sides with thebalanced reflectance coating. In contrast to the standardanti-reflection coating of the previous example, this coating (at thecentre of the lens) exhibits substantially lower photopic reflectance atlonger wavelengths. Indeed, it is anti-reflective beyond 880 nm. Whenthe coating thickness reduces away from the centre of the lens and thereflectance spectrum shifts to the left, relatively little intensity isintroduced in the red region of the spectrum. The CMC colour difference(for CIE illuminant C) between the centre of the lens and at the radiusof 20 mm is ΔE_(CMC(2:1))=10.

The lens displays relatively little colour roll-off, particularly in itshue. The lens changes from light blue (h*=292°) in the centre to paleblue/purple (h*=281°) at the radius of 20 mm. The luminous intensity ofthe reflection concurrently reduces from 3.4% to 1.8%.

The result is a coating that demonstrates substantially improved colouruniformity on highly curved substrates, without the requirement foradditional substrate motion during deposition.

TABLE 2 Optical design for a balanced reflectance anti-reflectioncoating Layer Thickness (nm) Hard resin substrate TiO2 (n(500 nm) =2.15) 15.9 SiO2 32.5 TiO2 (n(500 nm) = 2.15) 147 SiO2 102

EXAMPLE 3

Balanced Reflectance Anti-reflection Coating with Low Variation inLightness

Table 3 shows the optical design for another anti-reflection coatingwhose reflected colour is robust to colour roll-off when its thicknessvaries.

FIG. 3 compares the typical reflectance spectra measured at the centreand at a radius of 20 mm on a 16 dioptre polycarbonate lens coated onboth sides with the roll-off-resistant coating. (The spectra are theaverages of measurements taken on 27 different coated lenses.) The CMCcolour difference (for CIE illuminant C) between the centre of the lensand at the radius of 20 mm is ΔE_(CMC(2:1))=16.

The lens displays relatively little colour roll-off, particularly in itsluminance. The lens changes from pale green (h*=224°) in the centre topale blue/purple (h*=289°) at the radius of 20 mm. While the change inhue is noticeable, it is not unpleasant and is judged to be acceptablebecause the luminous intensity of the reflection concurrently reducesfrom 1.8% to only 1.2%.

TABLE 3 Optical design for a balanced reflectance anti-reflectioncoating Layer Thickness (nm) Polycarbonate substrate Abrasion-resistantcoating 2500 SiO2 18 Pr2O3/TiO2 (n(500 nm) = 2.05) 17.9 SiO2 36.7Pr2O3/TiO2 (n(500 nm) = 2.05) 140.2 SiO2 91.8

EXAMPLE 4

Balanced Reflectance Anti-reflection Coating with High Variation in Hue

Table 4 shows the optical design for another anti-reflection coatingwhose reflected lightness is robust to colour roll-off when itsthickness varies.

FIG. 4 illustrates the calculated reflectance spectrum for a CR39 lenscoated on both sides with the roll-off-resistant coating, as well as thereflectance spectrum when the coating thickness is reduced by 20%, asmay be the case on the edge of a highly curved lens or in a depositionsystem that produced coatings of highly non-uniform thickness.

The lens displays relatively little luminance roll-off, with theluminous intensity of the reflection reducing from 1.3% to only 0.9% asthe thickness of the coating is reduced by 20%. The lens changes fromdeep purple (h*=309°) through blue, to green (h*=164°). The change inhue is significant, yet despite these changes in hue, the lens remainshighly anti-reflective. Such a multicoloured anti-reflection coating aswould occur on a highly curved lens may be aesthetically pleasing.

TABLE 4 Optical design for a balanced reflectance anti-reflectioncoating Layer Thickness (nm) CR39 lens element substrate SiO2 18 TiO2(n(500 nm) = 2.15) 25.7 SiO2 20.1 TiO2 (n(500 nm) = 2.15) 118.7 Al2O3(n(500 nm) = 1.64) 15.7 SiO2 90.7

EXAMPLE 5

Balanced Reflectance Mirror Coating

Table 5 shows the calculated optical designs for mirror coatings whosereflectance is robust to colour roll-off when their thickness varies.The colour variations correspond to a thickness reduction of 20% and areclearly quite small.

FIG. 5 illustrates the corresponding calculated reflectance spectra fortinted CR39 lenses coated on the front surface with theroll-off-resistant coatings. It can be seen that the resistance tocolour roll-off has been achieved by designing the coating to display arelatively flat reflectance in the near infra-red spectrum, as opposedto a minimal infra-red reflectance as was the case for theroll-off-resistant anti-reflection coatings. In addition, the spectra donot display sharp structure in the visible wavelengths from 380-780 nm.

TABLE 5 Optical d signs for balanced refl ctance mirror coatings ColourBlue Gold Substrate CR39 CR39 Layer 1 24.4 nm TiO2 14.8 nm TiO2 Layer 220 nm SiO2 100 nm SiO2 Luminance, Y 11.6% 2.3% Hue, h* 270° 80°Luminance change, ΔY −2.4% 2.4% Hue change, Δh* 1° 15° Colourdifference, ΔE 2.4 12

What is claimed is:
 1. An optical lens with a coating varyingsubstantially in thickness from its center to a radius proximate itsedge but having substantially uniform color from its center to theradius proximate its edge comprising an ophthalmic lens element having acurved surface with a curvature from the center to the radius proximateits edge corresponding to at least 6 D; and an antireflection coating onthe curved surface of the lens element exhibiting a reflected colordifference (ΔE) from the center to the radius proximate the edge of thelens element of less than 11 CMC color difference units.
 2. A coatedoptical lens according to claim 1 wherein the lens element is ofgenerally ovaline we and curvature from the center to the radiusproximate its shape edge corresponds to 11 D or above.
 3. A coatedoptical lens according to claim 1 wherein the coating exhibits asubstantially low photopic reflectance in the red to infrared wavelength range of approximately 620 to 880 nm.
 4. A coated optical lensaccording to claim 3 wherein the substantially low photopic reflectanceis less than approximately 3%.
 5. A coated optical lens according toclaim 4 wherein the coating exhibits a substantially uniform appearancefrom the center to the radius proximate the edge of the lens element. 6.A coated optical lens according to claim 1 wherein, in use, the coatingexhibits a reflected color difference from the center to a radius ofapproximately 20 mm on the lens surface of less than approximately 11CMC color difference units or less.
 7. A coated optical lens accordingto claim 1 which coating includes a plurality of layers, the thicknessand/or number of which are selected to provide the substantially uniformcolor in response to visual effects generated by variations in thicknessof the coating.
 8. A coated optical lens according to claim 7 includinga plurality of layers of differing refractive index wherein thethickness and/or number of the respective layers are selected to balancethe variation of any combination of reflectance lightness, hue andchroma.
 9. A coated optical lens according to claim 8 where the layersof differing refractive index are formed from a dielectric materialselected from one or more of Al₂O₃, BaTiO₃, Bi₂O₃, B₂O₃, CeO₂, Cr₂O₃,Ga₂O₃, GeO₂, Fe₂O₃, HfO₂, In₂O₃, Indium-tin oxide, La₂O₃, MgO, Nd₂O₃,Nb₂O₅, Pr₂O₃, Sb₂O₃, Sc₂O₃, SiO, SiO₂, SnO₂, Ta₂O₅, TiO, TiO₂, TiO₃,WO₃, Y₂O₃, Yb₂O₃, ZnO, ZrO₂, AlF₃, BaF₂, CaF₂, CdF₂, CeF₃, HfF₄, LaF₃,LiF, MgF₂, NaF, Na₃AlF₆, NdF₃, PbF₂, PrF₃, SrF₂, ThF₄, ZrF₄, Si₃N₄, AlN,diamond-like carbon, polymeric dielectric materials or doped dielectricmartial.
 10. A coated optical lens according to claim 9 wherein thelower index layers include a silica (SiO₂) or magnesium fluoride (MgF₂)material.
 11. A coated optical lens according to claim 10 wherein thehigher refractive index layer(s) exhibit a refractive index ofapproximately 2.0 or greater.
 12. A coated optical lens according toclaim 11 wherein the higher refractive index layer(s) include a titaniumoxide (TiO₂) layer or a combination of titanium oxide (TiO₂) andpraseodymium oxide (Pr₂O₃).
 13. A coated optical lens according to claim12 including four to six alternating higher and lower refractive indexlayers of silica (SiO₂) and a titanium oxide (TiO₂) layer or acombination of titanium oxide (TiO₂) and praseodymium oxide (Pr₂O₃). 14.A coated optical lens according to claim 7 wherein the coating is formedof a plurality of dielectric and metallic layers wherein the thicknessand/or number of the respective layers are selected to balance thevariation of any combination of reflected lightness, hue and chroma. 15.A coated optical lens according to claim 14 wherein the dielectriclayer(s) is formed from a dielectric material selected from one or moreof Al₂O₃, BaTiO₃, Bi₂O₃, B₂O₃, CeO₂, Cr₂O₃, Ga₂O₃, GeO₂, Fe₂O₃, HfO₂,In₂O₃, Indium-tin oxide, La₂O₃, MgO, Nd₂O₃, Nb₂O₅, Pr₂O₃, Sb₂O₃, Sc₂O₃,SiO, SiO₂, SnO₂, Ta₂O₅, TiO, TiO₂, TiO₃, WO₃, Y₂O₃, Yb₂O₃, ZnO, ZrO₂,AlF₃, BaF₂, CaF₂, CdF₂, CeF₃, HfF₄, LaF₃, LiF, MgF₂, NaF, Na₃AlF₆,Na₅Al₃F₁₄, NdF₃, PbF₂, PrF₃, SrF₂, ThF₄, ZrF₄, Si₃N₄, AlN, ordiamond-like carbon, polymeric dielectric materials or doped dielectricmaterials; and the metallic layer(s) is formed from a metallic materialselected from the metals, metal oxides or metal nitrides of one or moreof Aluminum (Al), Chromium (Cr), Niobium (Nb), Nickel (Ni), Palladium(Pd), Tin (Su), Tantalum (Ta), Titanium (Ti), Tungsten (W), or Zirconium(Zr).
 16. A coated optical lens according to claim 14, wherein thecoating is a light absorbing asymmetric reflectance coating such thatfrom the wearer's side of the lens element the coating isanti-reflective.
 17. A coated optical lens of claim 1, wherein thecoating varies by at least 20% in thickness from its center to theradius proximate its edge.
 18. A multi-coated optical lens with at leastone coating varying substantially in thickness from center to edge buthaving a substantially uniform color from center to edge including anophthalmic lens element having a curved surface with a curvature fromthe center to a radius proximate its edge which corresponds to at least6 D; a first coating on the front surface of the lens element; and asecondary coating on the back surface of the lens element; the first andsecond coatings in combination exhibiting a reflected color difference(ΔE) from the center to the radius proximate the edge of the lenselement of less than 11 CMC color difference units.
 19. A multi-coatedoptical lens according to claim 18, wherein the secondary coatingfunctions to reduce optical aberrations generated by the first coating.20. A multi-coated optical lens according to claim 19, wherein thesecondary coating exhibits a difference in reflected brightness or huerelative to the first coating.
 21. A multi-coated optical lens accordingto claim 19, wherein the secondary coating exhibits a reflectance peakwhich is spectrally displaced with respect to a reflectance peak of thefirst coating.
 22. A coated optical lens of claim 18, wherein at leastone of the first and secondary coatings varies by at least 20% inthickness from its center to the radius proximate its edge.
 23. Anoptical lens with a coating varying substantially in thickness fromcenter to edge and having a visible, balanced change in color fromcenter to edge comprising: an ophthalmic lens element having a curvedsurface with a base curvature from the center to a radius proximate itsedge corresponding to at least 6 D; and an antireflection coating on thecurved surface of the lens element exhibiting a reflected colordifference (ΔE) from the center to the radius proximate its edge fromapproximately 11 to 20 CMC color difference units, wherein the colordifference is balanced by a complementary reduction in luminousintensity.
 24. A coated optical lens according to claim 23 wherein thecoating exhibits a reflected color difference (ΔE) from the center to aradius of approximately 20 mm on the lens surface of from approximately11 to 20 CMC color difference units.
 25. A coated optical lens of claim23, wherein the coating varies by at least 20% in thickness from centerto edge.
 26. A mirror-coated optical lens having a mirror coating whichexhibits a substantial variation in thickness from center to edge buthas substantially uniform color from center to edge comprising: anoptical lens element having a curved surface with a base curvature fromthe center to a radius proximate its edge corresponding to at least 11D; and wherein the mirror coating is on the curved surface of the lenselement and exhibits a reflected color difference (ΔE) from its centerto the radius proximate its edge of less than 11 CMC color differenceunits.
 27. A mirror coated optical lens according to claim 26 wherein,in use, the coating exhibits a reflected color difference from thecenter to a radius of approximately 20 mm on the lens surface ofapproximately 11 to 12 CMC color difference units.
 28. A coated opticallens of claim 26, wherein the coating varies by at least 20% inthickness from center to edge.